Ionic liquids

ABSTRACT

This invention relates to novel ionic liquids with the general formula [cation] [R′—SO 4 ] in which R′ is a branched or linear, saturated or unsaturated, aliphatic or alicyclic functionalized or non-functionalized hydrocarbon chain with 3-36 carbon atoms. These novel ionic liquids can be used e.g. as solvents or solvent additives in chemical reactions, as extraction agents or as heat carriers.

[0001] The present invention relates to novel ionic liquids with thegeneral formula [cation] [R′—SO₄], wherein R′ is a branched or linear,saturated or unsaturated, aliphatic or alicyclic, functionalized ornon-functionalized hydrocarbon chain with 3-36 carbon atoms. These novelionic liquids can be used e.g. as solvents or solvent additives inchemical reactions, as extraction agents or as heat carriers.

TECHNICAL CONTEXT OF THE INVENTION

[0002] The term ionic liquids should be understood to mean salts ormixtures of salts whose melting point is below 100° C. (P. Wasserscheid,W. Keim, Angew. Chem. 2001, 112, 3926). Salts of this type known fromthe literature consist of anions, such as halogenostannates,halogenoaluminates, hexafluorophosphates or tetrafluoroborates combinedwith substituted ammonium cations, phosphonium cations, pyridiniumcations or imidazolium cations. Several publications have alreadydescribed the use of ionic liquids as solvents for chemical reactions(T. Welton, Chem. Rev. 1999, 99, 2071, P. Wasserscheid, W. Keim, Angew.Chem., 2000, 112, 3926). For example, hydrogenation reactions of olefinswith rhodium(I) (P. A. Z. Suarez, 3. E. L. Dullius, S. Einloft, R. F. deSouza and J. Dupont, Polyhedron 15/7, 1996, 1217-1219), ruthenium(II)and cobalt(II) complexes (P. A. Z. Suarez, 3. E. L. Dullius, S. Einloft,R. F. de Souza and J. Dupont, Inorganica Chimica Acta 255, 1997,207-209) have been carried out successfully in ionic liquids withtetrafluoroborate anion. The hydroformylation of functionalized andnon-functionalized olefins is possible with rhodium catalysts in ionicliquids with weakly coordinating anions (e.g. PF₆ ⁻, BF₄ ⁻) (Y. Chauvin,L. Mussmann, H. Olivier, European Patent, EP 776880, 1997; Y. Chauvin,L. Mussmann, H. Olivier, Angew. Chem., Int. Ed. Engl., 1995, 34, 2698;W. Keim, D. Vogt, H. Waffenschmidt, P. Wasserscheid, J. of Cat., 1999,186, 481).

[0003] Further important fields of application of ionic liquids consistsof their use as extraction agents for material separation (J. G.Huddleston, H. D. Willauer, R. P. Swallows, A. E. Visser, R. D. Rogers,Chem. Commun. 1998, 1765-1766; b) A. E. Visser, R. P. Swatlowski, R. D.Rogers, Green Chemistry 2000, 2(1), 1-4) and of their use as heatcarrier (M. L. Mutch, J. S. Wilkes, Proceedings of the EleventhInternational Symposium on Molten Salts, P. C. Trulove, H. C. De Long,G. R. Stafford and S. Deki (Editors), Proceedings Volume 98-11, TheElectrochemical Society, Inc, Pennington, N.J.; 1998, page 254).

BACKGROUND AND FORMULATION OF THE PROBLEM INVOLVED

[0004] Even if the definition of an ionic liquid includes those saltswhose melting point is between the room temperature and 100° C. it isstill necessary and desirable for many applications for the ionicliquids to be liquid at temperatures below room temperature.

[0005] Numerous examples of such ionic liquids are known; however, as arule these systems possess halide ions such as F⁻, Cl⁻, Br⁻ or I⁻ orthose anions which contain halogen atoms. Typical representatives of thelatter anions are—without any claim to completeness —[BF₄]⁻, [PF₆]⁻,[CF₃COO]⁻, [CF₃SO₃]⁻, [(CF₃SO₂)₂N]⁻, [AlCl₄]⁻, [Al₂Cl₇]⁻ or [SnCl₃]⁻.The use of such anions containing halogen atoms imposes seriousrestrictions on the applicability of the corresponding ionic liquids: a)The use of these anions leads to considerable costs since even thealkali salts of these ions are very expensive; b) The hydrolysisproducts of these anions containing halogen atoms lead to considerablecorrosion in steel reactors and in some instances also in glassreactors; c) The thermal disposal of a “spent” ionic liquid with anionscontaining halogen atoms usually causes corrosion and environmentalproblems and is therefore very costly. The disposal via degradation in abiological clarification plant is also rendered difficult by thepresence of anions containing halogen atoms.

[0006] In general, those ionic liquids free from halogen atoms aretherefore of particular interest which combine the following fiveproperties:

[0007] a) a melting point and/or glass transition point of less than 25°C.;

[0008] b) hydrolysis-stable in neutral aqueous solution (pH=7) up to 80°C.;

[0009] c) to be disposed of by thermal means without the formation ofproblematic combustion gases

[0010] d) degradable in biological clarification plants

[0011] e) The anion is commercially available as alkali salt at afavorable price.

[0012] Among the ionic liquids free from halogen atoms according to thestate of the art, there have been no representatives so far capable ofsatisfying this complex technical requirement profile. Thus nitratemelts, nitrite melts, sulfate melts (J. S. Wilkes, M. J. Zaworotko, J.Chem. Soc. Chem. Commun. 1992, 965) and benzene sulfonate melts (H.Waffenschmidt, Dissertation, RWTH Aachen 2000) are known, however, theseionic liquids have melting points above room temperature. Hydrogensulfates and hydrogen phosphates react in aqueous solution whilesplitting off one or several protons and form acidic aqueous solutions.Methyl sulfate and ethyl sulfate melts exhibit a distinct hydrolysisafter only 1 h at 80° C. in aqueous solution with the formation ofhydrogen sulfate anions and the corresponding alcohol (compare alsocomparative examples 1 and 2).

OUR INVENTION AS A SOLUTION TO THE PROBLEM

[0013] Our invention is based on the surprising finding that ionicliquids consisting of a combination of a suitable organic cation—withimidazolium cations, pyridinium cations, phosphonium cations or ammoniumcations being particularly suitable examples—with anions with thegeneral formula [R—SO₄]—R being a linear or branched, saturated orunsaturated, aliphatic or alicyclic, functionalized ornon-functionalized alkyl radical with 3-36 carbon atoms—arecharacterized precisely by the above-mentioned, highly interesting andtechnically relevant combination of properties: The novel ionic liquidsaccording to the invention possess, on the one hand, a melting pointand/or glass transition point of less than 25° C., they are, moreover,hydrolysis-stable in neutral aqueous solution (pH=7) up to 80° C.Moreover, the ionic liquids according to this invention cause noproblems during thermal disposal since only CO₂, H₂O and SO₂ are formedduring their combustions. A further essential advantage of the novelionic liquids according to the invention is the fact that many alkalisalts with the general formula [alkalinization] [R—SO₄]—in which R is alinear or branched, functionalized or non-functionalized, saturated orunsaturated, aliphatic or alicyclic alkyl radical with 3-36 carbonatoms—are raw materials readily available in industry for detergents andfor products in the cosmetics and cleaning agents sector. This has leadto an extraordinarily high level of knowledge on the toxicologicalproperties and the biological degradation behavior of the anioncomponent [RSO₄]. From this, the conclusion can be drawn that thedisposal of the ionic liquids according to the invention “spent” intechnical applications can be carried out without problems in biologicalclarification plants.

[0014] The combination of these five properties, which, technicallyspeaking, is highly interesting, characterizes the novel ionic liquidsaccording to this invention as ideal solvents and/or solvent additivesfor stoichiometric or catalytic chemical reactions and for their use asextraction agents and as heat carriers.

[0015] Particularly preferably those ionic liquids, too, can be producedand used according to the invention which contain mixtures of differentanions with the general formula [RSO₄]—R being a linear or branched,saturated or unsaturated, aliphatic or alicyclic, functionalized ornon-functionalized alkyl radical with 3-36 carbon atoms. These systemscan be easily obtained from the mixtures of the corresponding alkalisalts which are available in industry.

[0016] In detail, the following novel ionic liquids according to theinvention and their mixtures deserve to be mentioned:

[0017] 1-ethyl-3-methylimidazolium butyl sulfate

[0018] 1-ethyl-3-methylimidazolium octyl sulfate

[0019] 1-ethyl-3-methylimidazolium 2-ethylhexyl sulfate

[0020] 1-ethyl-3-methylimidazolium dodecyl sulfate

[0021] 1-butyl-3-methylimidazolium butyl sulfate

[0022] 1-butyl-3-methylimidazolium octyl sulfate

[0023] 1-butyl-3-methylimidazolium 2-ethylhexyl sulfate

[0024] 1-butyl-3-methylimidazolium dodecyl sulfate

[0025] 1-hHexyl-3-methylimidazolium butyl sulfate

[0026] 1-hexyl-3-methylimidazolium octyl sulfate

[0027] 1-hexyl-3-methylimidazolium 2-ethylhexyl sulfate

[0028] 1-hexyl-3-methylimidazolium dodecyl sulfate

[0029] 1-octyl-3-methylimidazolium butyl sulfate

[0030] 1-octyl-3-methylimidazolium octyl sulfate

[0031] 1-octyl-3-methylimidazolium 2-ethylhexyl sulfate

[0032] 1-octyl-3-methylimidazolium dodecyl sulfate

[0033] 1-decyl-3-methylimidazolium butyl sulfate

[0034] 1-decyl-3-methylimidazolium octyl sulfate

[0035] 1-decyl-3-methylimidazolium 2-ethylhexyl sulfate

[0036] 1-decyl-3-methylimidazolium dodecyl sulfate

[0037] 1-dodecyl-3-methylimidazolium butyl sulfate

[0038] 1-dodecyl-3-methylimidazolium octyl sulfate

[0039] 1-dodecyl-3-methylimidazolium 2-ethylhexyl sulfate

[0040] 1-dodecyl-3-methylimidazolium dodecyl sulfate

[0041] 1-dodecyl-3-methylimidazolium tetrafluoroborate

[0042] 1-butyl-pyridinium butyl sulfate

[0043] 1-butyl-pyridinium octyl sulfate

[0044] 1-butyl-pyridinium 2-ethylhexyl sulfate

[0045] 1-butyl-pyridinium dodecyl sulfate

[0046] trimethyldecylammonium butyl sulfate

[0047] trimethyldecylammonium octyl sulfate

[0048] trimethyldecylammonium 2-ethylhexyl sulfate

[0049] trimethyldecylammonium dodecyl sulfate

[0050] trioctylmethylammonium butyl sulfate

[0051] trioctylmethylammonium octyl sulfate

[0052] trioctylmethylammonium 2-ethylhexyl sulfate

[0053] trioctylmethylammonium dodecyl sulfate

[0054] trimethyldecylammonium butyl sulfate

[0055] trimethyldecylammonium octyl sulfate

[0056] trihexyltetradecylphosphonium butyl sulfate

[0057] trihexyltetradecylphosphonium octyl sulfate

[0058] trihexyltetradecylphosphonium 2-ethylhexyl sulfate

[0059] trihexyltetradecylphosphonium dodecyl sulfate

EXAMPLES Example 1 1,3-Dimethylimidazoliumoctyl sulfate ([MMIM][OcSO₄])

[0060] Synthesis:

[0061] To a solution of 47.18 g (355.8 mmole) of 1,3-dimethylimidazoliumchloride ([MMIM] Cl) in 400 ml of methylene chloride rendered absolute,95.00 g (minimum 355.8 mmole) of sodium octyl sulfate (technical grade;content≧87%) are added in small portions. The batch is stirred for 40hours under blanketing gas. The solid is filtered off and washed withmethylene chloride. The organic phase is concentrated and dried under ahigh vacuum to give 87.55 g [MMIM][OCSO₄] (285.7 mmole; 80% of thetheoretical yield) in the form of a yellowish liquid.

[0062] NMR:

[0063]¹H-NMR (300 MHz, d⁶-DMSO): δ=8.87 (s, 1H, N—CH—N), 7.45, 7.44 (ones in each case, 1H in each case, N—CH), 3.87 (mult., 8H, N—CH₃,S—O—CH₂—), 1.57 (mult., 2H, S—O—CH₂—CH₂—), 1.29 (k.B., 10H,S—O—CH₂—CH₂—CH₂—(CH₂)₅—), 0.89 (t, 3=6.6 Hz, 3H, —CH₂—CH₃) ppm,

[0064]¹³C-NMR (75 MHz, d⁶-DMSO): δ=136.7, 122.8, 116.8, 35.1, 30.9,28.7, 28.4, 25.1, 21.7, 12.8 ppm,

[0065] Viscosity:

[0066] The product exhibits a structural viscosity. The viscosity isstrongly dependent on the conditions of measurement.

Example 2 1-n-Butyl-3-methylimidazoliumoctyl sulfate ([BMIM][OCSO₄])

[0067] Preparation:

[0068] 84.55 g (0.484 mole) of 1-butyl-3-methylimidazolium chloride(BMIM Cl) and 101.1 g (minimum 0.379 mole) of sodium octyl sulfate(technical grade; content ≧87%) are dissolved in 200 ml of hot water.The water is slowly removed under vacuum. The solid formed is filteredoff after dissolving the batch in methylene chloride. The filtrate iswashed until the aqueous phase is colorless and free from chloride. Theorganic phase is dried over Na₂SO₄. Concentrating and drying under ahigh vacuum gives 111.0 g (0.319 mmole; 73% of the theoretical yield,based on sodium octyl sulfate) of an oily yellow liquid.

[0069] NMR

[0070]¹H-NMR (300 MHz, d⁶-DMSO): δ=9.16 (s, 1H, N—CH—N), 7.80, 7.72 (sin each case, 1H in each case, N—CH), 4.18 (t, 33=7.1 Hz, 2H, N—CH₂—),3.86 (s, 3H, N—CH₃), 3.71 (t, ³J=6.6 Hz, 2H, S—O—CH₂), 3.71 (p, 3J=7.3Hz, 2H, N—CH₂—CH₂—), 1.47 (k.B., 2H, N—CH₂—CH₂—CH₂—), 1.22 (mult.,12H,S—O—CH₂—(CH₂)₆—), 0.81-0.90 (each tr, each 3H, —CH₃) ppm.

[0071]¹³C-NMR (75 MHz, d⁶-DMSO): δ=136.9, 123.9, 122.6, 66.0, 55.2,48.8, 36.0, 31.8, 31.6, 29.4, 29.1, 25.9, 22.4, 19.1, 14.2, 13.5 ppm.

[0072] Viscosity

[0073] η(20° C.)=711 cP

Example 3 1-n-Butyl-3-methylimidazolium lauryl sulfate([BMIM][C₁₂H₂₅SO₄])

[0074] Synthesis:

[0075] 15.30 g (87.6 mmole) of 1-n-butyl-3-methylimidazolium chloride(BMIM Cl) and 26.60 g (minimum 87.6 mmole) of sodium lauryl sulfate(technical grade, content 95-99%) are dissolved in 50 ml of hot water.The water is slowly removed under vacuum. The solid formed is filteredoff after adding methylene chloride to the batch. The filtrate is washedwith water until the aqueous phase is colorless and free from chloride.The organic phase is dried over Na₂SO₄. Concentrating and drying under ahigh vacuum gives 33.40 g of product (82.5 mmole; 94% of the theoreticalyield, based on BMIM Cl) which is obtained as a white beige waxy solid.

[0076] Melting point: 44-45° C.

[0077] NMR:

[0078]¹H-NMR (300 MHz, CD₃CN): δ=8.76 (s, 1H, N—CH—N), 7.43, 7.40 (twos, 1H in each case, N—CH₃), 4.17 (t, J=7.3 Hz, 2H, N—CH₂), 3.87 (s, 3H,N—CH₃), 3.83 (t, J=6.6 Hz, 2H, S—O—CH₂—), 1.84 (mult., 2H, N—CH₂—CH₂—),1.58 (mult., 2H, S—O—CH₂—CH₂—), 1.40-1.25 (mult., 20H,S—O—CH₂—CH₂—(CH₂)₉—; N—CH₂—CH₂—CH₂—), 1.00-0.85 (t, each 3H, —CH₃) ppm.

[0079]¹³C-NMR (75 MHz, CD3CN): δ=136.2, 123.3, 121.9, 65.9, 48.9-48.7,35.4, 31.3, 29.1-28.7, 25.5, 22.1, 18.6, 13.1, 12.4 ppm.

[0080] Hydrolysis Tests

Example 4 Hydrolysis Test with 1-n-butyl-3-methylimidazoliumoctylsulfate ([BMIM][C₈H₁₇SO₄])

[0081] To 5 g of the ionic liquid of 1-n-butyl-3-methylimidazoliumoctylsulfate ([BMIM][C₈H₁₇SO₄]), 5 ml of water are added and heated to 80° C.At intervals of 10 min, samples are taken from the reaction solution andpH measurements are carried out. The reaction solution is stillpH-neutral after 2h at 80° C. which suggests that no hydrolyticdecomposition of the ionic liquid takes place under these reactionconditions.

Comparative Example 1 Hydrolysis Test with 1-n-butyl-3-methylimidazoliumMethyl Sulfate ([BMIM][CH₃SO₄])

[0082] To 5 g of the ionic liquid of 1-n-butyl-3-methylimidazoliummethyl sulfate ([BMIM][CH₃SO₄]), 5 ml of water are added and heated to80° C. At intervals of 10 min, samples are taken from the reactionsolution and pH measurements are carried out. The reaction solutionexhibits a rapid decrease in the pH to 1-2 after the first measurement.This suggests that, under these reaction conditions, a hydrolyticdecomposition of the ionic liquid takes place. Methanol and the acidichydrogen sulfate anion are liberated during this process.

Comparative Example 2 Hydrolysis Test with1-ethyl-3-methylimidazoliumethyl Sulfate ([EMIM][C₂H₅SO₄])

[0083] To 5 g of the ionic liquid of 1-ethyl-3-methylimidazoliumethylsulfate ([EMIM][C₂H₅SO₄]), 5 ml of water are added and heated to 80° C.At intervals of 10 min, samples are taken from the reaction solution andpH measurements are carried out. The reaction solution exhibits a rapiddecrease in the pH to 1-2 after the first measurement. This suggeststhat, under these reaction conditions, a hydrolytic decomposition of theionic liquid takes place. Ethanol and the acidic hydrogen sulfate anionare liberated during this process.

The following is claimed:
 1. An ionic liquid with the general formula [cation] [R′—SO₄] in which R′ is a linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl group with 3-36 carbon atoms which is non-functionalized or functionalized with one or several X groups and X represents an —OH, —OR″, —COOH, —COOR″, —NH₂, —SO₄, —F, —Cl, —Br, —I or —CN group, R″ being a branched or linear hydrocarbon chain with 1-12 carbon atoms.
 2. The ionic liquid according to claim 2 characterized in that the [cation] used represents a quaternary ammonium cation with the general formula [NR₁R₂R₃R]⁺, phosphonium cation with the general formula [PR₁R₂R₃R]⁺, imidazolium cation with the general formula

in which the imidazole core may be substituted with at least one group selected from C₁-C₆ alkyl groups, C₁-C₆ alkoxy groups, C₁-C₆ aminoalkyl groups, C₅-C₁₂ aryl groups or C₅-C₁₂-aryl-C₁-C₆ alkyl groups, pyridinium cations with the general formula

in which the pyridine core may be substituted with at least one group selected from C₁-C₆ alkyl groups, C₁-C₆ alkoxy groups, C₁-C₆ aminoalkyl groups, C₅-C₁₂ aryl groups or C₅-C₁₂-aryl-C₁-C₆ alkyl groups, pyrazolium cations with the general formula

in which the pyrazole core may be substituted with at least one group selected from C₁-C₆ alkyl groups, C₁-C₆ alkoxy groups, C₁-C₆ aminoalkyl groups, C₅-C₁₂ aryl groups or C₅-C₁₂-aryl-C₁-C₆ alkyl groups, and triazolium cations with the general formula

in which the triazole core may be substituted with at least one group selected from C₁-C₆ alkyl groups, C₁-C₆ alkoxy groups, C₁-C₆ aminoalkyl groups, C₅-C₁₂ aryl groups or C₅-C₁₂-aryl-C₁-C₆ alkyl groups, and the radicals R1, R2, R3 are selected independently of each other from the group consisting of hydrogen; linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups with 1 to 20 carbon atoms; heteroaryl groups, heteroaryl-C₁-C₆ alkyl groups with 3 to 8 carbon atoms in the heteroaryl radical and at least one heteroatom selected from N, O and S, which may be substituted with at least one group selected from C₁-C₆ alkyl groups and/or halogen atoms; aryl groups, aryl-C₁-C₆ alkyl groups with 5 to 12 carbon atoms in the aryl radical, which may optionally be substituted with at least one C₁-C₆ alkyl group and/or a halogen atom; and the radical R is selected from linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups with 1 to 20 carbon atoms; heteroaryl-C₁-C₆ alkyl groups with 3 to 8 carbon atoms in the aryl radical and at least one heteroatom selected from N, O and S, which may be substituted with at least one C₁-C₆ alkyl group and/or halogen atoms; aryl-C₁-C₆ alkyl groups with 5 to 12 carbon atoms in the aryl radical, which may optionally be substituted with at least one C₁-C₆ alkyl group and/or halogen atoms;
 3. The ionic liquid according to claims 1 and 2 characterized in that the ionic liquid carries an anion with the empirical formula [C₄H₉SO₄].
 4. The ionic liquid according to claims 1 and 2 characterized in that the ionic liquid carries an anion with the empirical formula [C₈H₁₇SO₄].
 5. The ionic liquid according to claims 1 and 2 characterized in that the ionic liquid carries an anion with the empirical formula [C₁₂H₂₅SO₄].
 6. A chemical reaction in which an ionic liquid defined by claims 1-5 is used as solvent, solvent additive or phase transfer catalyst.
 7. The chemical reaction according to claim 6 characterized in that the reaction is a reaction catalyzed by a transition metal.
 8. The chemical reaction according to claims 6 or 7 characterized in that the reaction belongs to a group of reactions comprising hydroformylation reactions, oligomerization reactions, esterifications, isomerization reactions and reactions for amide bond linkage.
 9. The chemical reaction according to claim 6 characterized in that the reaction is a reaction catalyzed by an enzyme or by another biocatalyst.
 10. The chemical reaction according to claims 6 and 9 characterized in that the reaction belongs to a group of reactions comprising oligomerization reactions and other C—C bond linkage reactions, esterifications, isomerization reactions and reactions for amide bond linkage.
 11. A material separation process using, as solvent or solvent additive, an ionic liquid defined by claims 1-5.
 12. An apparatus for heat exchange in which an ionic liquid defined by claims 1-5 is used as heat carrier or heat carrier additive.
 13. A use of an ionic liquid according to claims 1-5 as solvent.
 14. The use of an ionic liquid according to claims 1-5 as solvent additive.
 15. The use of an ionic liquid according to claims 1-5 as phase transfer catalyst.
 16. The use of an ionic liquid according to claims 1-5 as solvent extraction agent.
 17. The use of an ionic liquid according to claims 1-5 as heat carrier. 